Overload protective system with resistance operated relay



Aug. 30, 1932. H 1,373,959

OVERLOAD PROTECTIVE SYSTEM WITH RESISTANCE OPERATED RELAY Filedflac. 12, 1924 Patented Aug. 30, 1932 UNITED STATES PATENT OFFICE ERNST HERMANN FREY, OF BADEN, SWITZERLAND, ASSIGNOR TO AKTIENGESELL- SCHAFT BROWN, BOVERI AND (HE, OF BADEN, SWITZERLAND OVERLOAD PROTECTIVE SYSTEM WITH RESISTANCE OPERATED RELAY Application filed December 12, 1924, Serial No. 755,581, and in Germany December 15, 1928.

In the case of overload protective systems which are to operate selectively, relays whose operation depends upon the magnitude of the resistance in the defective part of the line are I frequently used to determine the tripping time delay. In the case of short circuits, such relays cause those switches which are nearest to the point where the short circuit occurs to operate first. As, however, the relays should of course operate only when a short circuit occurs, they are commonly used in combination with auxiliary relays operating responsively to a function of the current. When a certain pre-determined current is ex- 16 ceeded, such an auxiliary relay might, for

example, close a circuit of the resistance dependent relay, or release a mechanical interlock of the resistance dependent relay, or put into action a delayed mechanism whose time lag is fixed by the resistance dependent relay.

All these arrangements are likely to fail in the case of a short circuit in a system on light load, which is being supplied by only a small portion of the available sources of current, if

25 this occurs at a point remote from the source of current. In such a case it may happen that the short circuit current is not even as high as the normal current at the point where the disturbance occurred, so that the current 80 operated i. e. overload auxiliary relays fail to operate. It is nevertheless necessary to switch out the short circuit as the line voltage in its neighbourhood is reduced to zero and consequently the current supply is disturbed in the whole district in the vicinity of the place where the short circuit occurred.

It has been found that this drawback can be avoided by using a device in which the resistance dependent relays are employed, not

- 40 only to fix the time lag of the protective device, but also in place of the usual current operated auxiliary relays to set the protective device in operation. The resistance dependent relays may be provided with a second contact, in addition to the tripping contact proper, which is actuated as soon as the line resistance (upon which the action of the relay depends) has reached a certain value, and which closes the circuit and causes a relay having a definite time limit to operate. After the elapse of a time limit determined by the setting of the resistance dependent relay, this definite time limit relay is allowed to actuate the tripping contact in the well known manner.

The drawing illustrates diagrammatically one way of arranging the relays and their connections for carrying the invention into effect.

In the figure a and b are movable coils connected to each other and fixed on shaft 10, c is the fixed coil of a relay device j designed on the principle of an ohmmeter, d is the switch, the time lag in the operation of which is set by the relay, and which serves to cut out the line section 6. The coils a and 0 are supplied by the current transformer f through which passes the current flowing in this section, the coil 12 being supplied by voltage prevailing in the section via the voltage transformer g. The supporting shaft 10 of the coils a and I) carries two contact devices, viz. the cam or element h and the contact arm Z.

A time limit relay device is comprises the member 11 carrying contacts 71 and which is rotated in the direction of the arrow 12 at a uniform rate on the pivot or spindle 13 by suitable clock mechanism or the equivalent, the latter being released, upon excitation of the electromagnet m, by any suitable means such as the interlock designated generally by reference numeral 1 1-.

The relay device 7' is responsive to the impedance of the line section 6, and upon occurrence of fault such as a short-circuit operates to rotate or adjust the angular position of the element or cam h in the direction of the arrow 15 and in amount inversely proportional to the impedance, or in other words, inversely proportional to the distance from the switch or breaker (Z to the point of the fault. As the point of the fault approaches breaker d, therefore, the element or cam b will be positioned correspondingly further to the right to permit of engagement of contacts 11 with the cam within a correspondingly smaller period of time from the instant of releasing action of interlock 14, in the manner and for the purpose hereinafter explained.

- therotary element or'camh.

The contact arm Z may either lie against the spring supported contact 9, or the spring supported contact p, or be allowed to move freely in the space between the two contacts. Under normal line conditions, the relay is either in the position where the contact Z touches the opposite contact p (with current in positive direction) or in the position where the contact Z touches the opposite contact 9 (with reverse current). Consequently one of the two parallel connected contacts p and g is always closed. If, however, a short circuit occurs, the resistance dependent relay device j moves to 'a position where the contact Z does not touch either of the two counter-contacts p and g, as shown, and changes the angular position of cam 7?. to the right by an amount inversely. proportional to the resistance, or inversely proportional to the distance between the breaker and the point of short circuit or other fault. :Tliusthe electro-magnet m s nserted n the circuitof the current transformer f. lhe electro-magnet then re- I leases the interlock 14 of the time limit relay device 7a, thereby causing an arm with the two contacts i tomove towards the cam IL. As soon as th1spa1r of contactstouches the rimof the cam, it closes the circuit of the current supply 0 over the tripping 0011 11,

thereby tripping the switch 03.

From the foregoing it will be seen that an improved protective system has been provided wherein the time elapsing between the occurrence of the short-circuit or other fault and the opening of the breaker is directly proportional to the distance between the latter and the point of the fault, such time being controlled by varying the angular position of Vfhatl claim is v V 1. A. selectivelyacting protective device including a resistance, dependent relay and a delay action relaycharacterized by the fact that the resistance dependent relay both sets into operation and regulates the time lag of the delayedaction relay.

2. In a protectivesystem, the combination .of a line, a protective'relay device for said line comprising a relay element responsive to the l ne impedance, and a. time-delay element, said impedance-responsive element controlling the initiation of the action of said time-delay element and the time lag of saidtime-delay element.

3. A protective relay device comprising an impedance-responsive relay element, and a time-dela relay element, said impedance responsive element controlling the initiation of the action of said time-delay element and the time delay efiected thereby.

4. In a protective relay device, control circuit terminals, a time-delay action relay element for operating said control circuit ter- 1 .aninals, and an impedance-respons1ve relay element for initiating the action of said timeof its action on said control circuit terminals.

5. In a protective system, the combination of a line, a control circuit therefor, a protective relay device for operating said control circuit, an element responsive tothe impedance of said lineforinitiating the action of said relay device on occurrence of predetermined line impedance conditions, and means responsiveto said impedance as determined by said element for determining the time lag required to carry out the control operation of said relay device on said control circuit.

6. In a system of thecharacter described, an electrical transmission I line, a circuit: breaker therefor, a time-delay element, an actuating element for initiating movement of the ti1ne-delay element to control actuation ofsaid circuit breaker, and means for determining the length of time during which said time-delayelement moves from the moment of initiation of its movement to the carrying out of the same, the operation of said actuating element and said means being responsive to the ratio of the line voltage to the line current, and the rate of move-H ment of thesaid time-delay element being in dependent of said actuating element and said means.

7. In combination, a relay including relatively movable cooperating members, and. means for controlling said members including an ohmmeter, a timing element, and ohmmetrically controlled means for controlling the starting of said timing element.

8. In a system of the character described, an electrical transmission line, a circuit 1 breaker therefor, a time-delay element, an element operable to control initiation of movement of'said time-delay elementto control actuation of said circuit breaker, means, i for determining the length of time during'ilo which said time-delay element moves from the moment of initiation of movement thereof to the carryingout ofthe same, and an element actuated responsive to and in depend-, encesolely on the ratio ofvoltage to current of said line. for operating saidmeans and for causing operation of the second said element. 7 l

V 9. Ina system of the character described, an electrical transmission line, a circuit flbreaker therefor, a time-delay element, an

element operable to control initiation of movement of said time-delay element to control actuation of said circuit breaker, means. for determining the length of time during which said time-delay element moves from the moment of initiation of movement thereof 

